In Reply Both letters suggest misunderstandings about the scientific goal of the task force, which was to explore the predictive validity of diagnostic criteria for sepsis. There is no gold standard for sepsis, which precludes simple measures of validity based on the presence of true positives (cases with sepsis) and true negatives (controls without sepsis). Predictive validity permits assessment of the extent to which potential criteria, applied in a population at risk of the unmeasurable condition (sepsis), predict outcomes more common in the condition.